(1) Field of the Invention
This invention relates to a rack and pinion gearing which can prevent the occurence of "biting" in a rack and pinion type steering mechanism for vehicles and other apparatus.
(2) Prior Art
Taking as an example the rack and pinion type steering mechanism for vehicles disclosed in U.S. Pat. No. 3,433,501 patented on Mar. 18, 1969, various problems attendant a rack and pinion gearing including a rack formed with helical gear-teeth and pinion with spiral gear-teeth are described hereinbelow.
In FIG. 6, of the accompanying drawings a rack and pinion gearing 60 comprises a rack 63 and a pinion 64, through which mechanism a rotational motion transmitted from a steering wheel 61 is converted into a reciprocal linear motion of a rod 62. The rack and pinion gearing of this kind generally used in power steering mechanism performs not only the function of reciprocating the rod 62 linearly for controlling a hydraulic circuit of a power steering device (not shown) but also that of advancing or retreating a control valve (not shown) a minute distance in the axial direction of the steering wheel 61 according to the rotation of a steering shaft 65. To achieve these functions, as shown in FIG. 6, the rack 63 with helical gear-teeth 66 and the pinion 64 with spiral gear-teeth 67 are so arranged that the spiral gear-teeth 67 may intermesh with the helical gear-teeth 66. FIG. 7 is an enlarged view showing this intermeshing. As the steering shaft 65 is rotated, one spiral gear-tooth 67 is brought into contact with a helical gear-tooth 66 of the rack 63 at one point and the rotation of the pinion is converted into a transverse movement of the rack 63 through interaction therebetween at this point. As a result, the pinion 64 with spiral gear-teeth 67 receives a force at the above point of action in the advance or retreat direction.
At such point of contact between the rack and pinion, there often occurs an undesirable "biting" effect. The terminology biting as employed herein relates to the action of the spiral gear-tooth 67 of pinion 64 intermeshing between two adjacent helical gear-teeth 66 of rack 63 and tightly wedging itself therebetween. The aforesaid biting results when, as the point of contact between the helical gear-tooth 66 and the spiral gear-tooth 67 shifts, a moment of rotation is produced about the axis of the rack 63, thereby causing the rack 63 to slightly incline or rock, as shown in FIG. 7. Particularly when the steering wheel 61 is turned while such vehicle is stopped, the biting may undesirably prevent the steering wheel 61 from returning easily, because a force component tending to rotate the pinion 64 becomes maximum at such time thus causing the pinion 64 to bite into the rack 63 with an extremely great force. Furthermore, in a power steering mechanism wherein a control valve for a power-assisting hydraulic cylinder is operated making use of rotational force or transverse movement of the pinion 64, there is usually provided an element for preventing the rack 63 from rocking, such as a spring 68 on the lower side of the rack 63 as shown in FIG. 7, so that the movement of the pinion 64 may be kept from being disturbed by the rocking of the rack 63. Such arrangement, however, leads to drawbacks such as increase in the numbers of elements and production processes, rise in cost and fall of productivity.
The present invention is directed toward effectively solving the foregoing problems attendant conventional rack and pinion arrangements.